1. Field of the Invention
This invention relates generally to a continuity tester and, more particularly, to a continuity tester including a specially configured conductive brush that has particular application for inspecting insulation damage on stator windings in an electric machine.
2. Discussion of the Related Art
Various types of electric machines are employed in vehicles to provide certain vehicle operations. For example, electric vehicles or electric hybrid vehicles employ traction motors that are often three-phase electric machines including a stator having a series of circumferentially disposed slots and a rotor having a series of circumferentially disposed conductors. Electrical windings are provided within the stator slots in a configuration to provide the three separate circuits for the three phases, where the windings may include conductive bars positioned in the slots. The conductive bars include an outer insulating layer typically formed by depositing multiple coatings of a non-conductive material.
During assembly of electric machines of this type, workers will handle the stator to configure and connect the various machine elements in an assembly process. During handling, the stator may be inadvertently bumped or rubbed against assembly equipment and other things, where nicks, cuts, abrasions and other defects sometimes occur in the insulation of the stator windings, which could expose the conductive part of the winding. For example, once the stator is assembled, the process of positioning the rotor within a central bore of the stator may damage the stator windings at various locations. Such defects in the insulation of the stator windings sometimes affect machine performance and could result in an unacceptable shorter machine life.
Various inspection operations can be performed to identify damage and defects to the insulation of the stator windings. For example, visual inspections can be performed where a quality control technician using a magnifying glass looks for defects in the insulation. Such an inspection operation is obviously labor intensive, and is subject to the limitations of the technician. It is also known in the art to employ a continuity tester that provides an electrical current through the stator windings, where the circuit is continuous at the location where the defect in the insulation occurs. Some continuity testers employ significantly high voltages to ensure that small defects are detected. However, known continuity testers, including those having a conductive brush, can be improved upon to increase the ability to safely detect smaller defects, provide automated testing, provide faster response times, etc.